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Abstract

All cells possess a molecular circadian ?clock? thought to coordinate various aspects of the physiology and behavior of an animal with the light/dark cycle of the external world. Light is the principle cue entraining molecular clocks via the suprachiasmatic nucleus of the brain. Recent evidence however, has also implicated food-borne signals as external stimuli capable of resetting clocks in the periphery. The aim of this study was to investigate the impact of aberrant feeding on circadian energy metabolism in the rat by feeding a high fat diet and restricting feeding to the daylight hours. Here we show that rats on the daylight feeding and high-fat feeding schedules displayed various differences in metabolism including hormone and metabolite levels and gene and protein expression. In the liver the circadian expression pattern of molecular clock genes was completely reversed in response to the new feeding schedule. In contrast, circadian gene expression in muscle remained similar to an animal feeding ad libitum. This asynchrony in circadian gene expression in two metabolically relevant tissues was accompanied by loss of diurnal variation and a reduction in energy expenditure, and increased muscle glycogen in the day-fed rats. These results indicate the importance of feeding cues in regulating circadian metabolism and overall energy homeostasis.